The substituent guest effect on four-step spin-crossover behavior?

Inorganic Chemistry Frontiers Pub Date: 2019-12-24 DOI: 10.1039/C9QI01420A

Abstract

Until now, the synthesis of new multi-step spin-crossover (SCO) materials is still a great challenge although they have attracted significant attention due to their potential applications in high-order data storage and multi-switches. Here, based on the four-step SCO complex [Fe(dpoda){Ag(CN)2}2]·1.5naph (1·1.5naph, dpoda = 2,5-di-(pyridyl)-1,3,4-oxadiazole, naph = naphthalene), the strategy of incorporating a substituent on an aromatic guest is applied. Since the replacement of H with an F atom can be regarded as isosteric substitution, the introduction of the 2-fluoronaphthalene (Fnaph) guest does not give rise to large structural changes and the four-step SCO behavior is maintained in 1·1.5Fnaph; however, fine-tuning of the framework is indeed achieved by the fluoro substituent. The spin transition temperatures of 1·1.5Fnaph shift to the low-temperature region, which should be due to the contributions of the size effect and the decrease in the Fe–N[triple bond, length as m-dash]C angle. Meanwhile, the thermal hysteresis loop disappears, which results from the competitive contributions of the π?π and F?Ag interactions. Therefore, the F substituent on the guest can effectively modify the four-step SCO behavior, which provides a simple solution to synthesize more multi-step SCO materials.

Graphical abstract: The substituent guest effect on four-step spin-crossover behavior
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